Conventional techniques for forming airlaid webs of fibrous material have employed drum formers with contoured forming screens located on the surface of the drum. For example, see U.S. Pat. No. 4,666,647 issued May 19, 1987 to Enloe et al. and U.S. Pat. No. 4,761,258 issued Aug. 2, 1988 to Enloe. Conventional techniques have also formed airlaid fibrous webs on a belt-type forming screen. For example, see U.S. Pat. No. 4,927,582 issued May 22, 1990 to Bryson.
It has been desirable to produce three-dimensional, contoured shapes in the fibrous webs formed on the surface of an endless-belt-type of forming screen. It has, however, been difficult to reliably form such shapes on a belt-type of forming system. If the forming belt is constructed with three-dimensional contour shapes formed therein, the shaped contours inhibit the movement of the endless belt screen around the turn rolls positioned at the ends of the apparatus. If the contoured shapes are molded within a relatively thick, forming screen belt, it has been difficult to reliably articulate the thick belt structure to allow high speed movement around the turn rolls positioned at the ends of the belt.
To form the desired three-dimensional shapes, conventional systems have also incorporated scarfing rolls having a peripheral scarfing surface which is contoured along the axial, length dimension of the scarfing rolls. Such scarfing rolls have been able to contour the basis weight distribution along the cross-direction of the fibrous web.
To contour the shape and basis weight distribution along the longitudinal, machine-direction of the web, some conventional techniques have incorporated an eccentrically-shaped displacement roller to selectively move the belt-type forming screen and reposition the fibrous web to thereby generate three-dimensional contours and a variable basis weight distribution along the machine-direction of the fibrous web. For example, see U.S. Pat. No. 4,690,853 issued Sep. 1, 1987, to P. Hammond.
Conventional techniques, such as those described above, have not adequately generated desired machine-direction contours and basis weight distributions along the lengthwise dimension of a fibrous web. Techniques which deform or deflect the forming screen can place additional, undesired stresses on the forming screen. The techniques may also be speed limited since inertia can prevent the screen from accurately following the contours of the deflecting roll. Other techniques, which intermittently displace a vertical positioning of the scarfing roll, may also be speed limited due to the inertia of the scarfing roll mechanism. Such conventional techniques have also been less able to form relatively abrupt changes in the basis weight distribution along the machine direction. As a result, there has been a continued need for an improved technique for selectively varying the basis weight distribution along the lengthwise, machine-direction of a fribrous web, such as a fibrous web composed of airlaid wood pulp fluff.